Analysis of Welding Stability of Dual-Coated Electrode Wear-Resistant Surfacing Electrodes

Literature Overview

This paper, published in Transactions of the China Welding Institution (焊接学报) in 2013, Volume 34, Issue 6, pages 25-28, investigates the welding stability of dual-coated electrode (dual-core) wear-resistant surfacing electrodes with a diameter of 4.0 mm. The authors, Zhao Wei, Zou Yong, Zou Zengda, and Wang Yufu from Shandong University's Key Laboratory of Liquid-Solid Structure Evolution and Processing, were supported by the National Natural Science Foundation of China (51171093). The study focuses on the influence of electrode parameters and welding process parameters on arc voltage and welding stability, which are critical for achieving consistent surfacing quality.

Core Technical Approach and Process Parameters

The dual-coated electrode design incorporates two coated cores within a single electrode, which is intended to improve arc stability and deposition uniformity compared to conventional single-core electrodes. The following table summarizes the key parameters investigated:

The dual-core design is a relatively novel approach to surfacing electrode design, and this study provides valuable insight into the fundamental parameters that govern its performance.

Arc Voltage and Dual-Core Spacing Analysis

The most significant finding of this study is that the arc voltage in dual-coated electrode welding is primarily determined by the spacing between the two cores. When the dual-core spacing is too small, the two arc zones overlap excessively, leading to arc instability and uneven deposition. When the spacing is too large, the arcs operate independently, resulting in poor arc stability and reduced deposition efficiency. At the optimal spacing of 1.0 mm, the arc voltage stabilizes at approximately 33 V, and welding stability is excellent.

This finding has important implications for electrode manufacturing. The core spacing must be precisely controlled during electrode production, as even small deviations can significantly affect welding performance. The arc voltage of 33 V is notably higher than that of conventional single-core electrodes of the same diameter, which typically operate at 22-28 V. This higher arc voltage is a direct consequence of the increased arc length created by the dual-core geometry.

Coating Weight Factor and Metallurgical Quality

The coating weight factor, defined as the ratio of coating weight to total electrode weight, plays a critical role in determining the protective gas generation, slag formation, and alloying element delivery. The study found that a coating weight factor of 45%-56% provides optimal protection, sufficient metallurgical reactions, and stable welding. Below this range, the coating is insufficient to provide adequate shielding and alloying, leading to porosity and reduced hardness. Above this range, the excessive coating can cause arc instability, increased spatter, and poor fusion with the base metal.

The surfacing layer hardness achieved with optimal parameters exceeds 6200 HV (approximately HRC 70+), which is characteristic of high-carbon high-chromium or carbide-containing surfacing alloys. This hardness level is sufficient for severe abrasive wear applications, including mining equipment, cement mill components, and pipeline handling equipment.

Welding Current and Electrode-to-Workpiece Distance

The optimal welding current range of 180-200 A is notably higher than that of conventional 4.0 mm surfacing electrodes, which typically operate at 120-160 A. This higher current requirement is attributed to the dual-core geometry, which effectively increases the electrode cross-section and requires more current to achieve adequate melting and deposition. The narrow current range (20 A) compared to conventional electrodes (40 A) reflects the sensitivity of the dual-core design to current variations, which must be carefully controlled to maintain arc stability.

The optimal electrode-to-workpiece distance of 7 mm is consistent with conventional surfacing electrode practice, but the study confirms that this distance provides good fusion between the surfacing layer and the base metal while maintaining arc stability. Deviations from this distance can lead to arc blow, poor fusion, or excessive spatter.

Engineering Practice Implications

For engineers considering the use of dual-coated surfacing electrodes, this study provides critical guidance on process parameter selection. The following practical recommendations can be derived:

1. Core spacing control: The electrode manufacturer must maintain the dual-core spacing at 1.0 mm with tight tolerances. Any deviation will affect arc voltage and stability.
2. Current setting: The welding current should be set within the 180-200 A range for 4.0 mm electrodes. Power sources with fine current adjustment capability are recommended.
3. Coating integrity: The coating weight factor must be maintained at 45%-56%. Coating damage during handling or storage should be inspected and rejected.
4. Travel technique: The electrode-to-workpiece distance should be maintained at approximately 7 mm. Consistent travel speed and angle are essential for uniform deposition.
5. Preheating: For thick sections or high-carbon base metals, preheating may be necessary to reduce the risk of cracking in the heat-affected zone.

In the context of steel pipe manufacturing and pipeline maintenance, dual-coated surfacing electrodes could be particularly useful for protecting pipe ends, flange faces, and coupling surfaces from abrasive wear during handling and installation. The high hardness achieved (>6200 HV) provides excellent protection against abrasive wear from sand, grit, and other particulate contaminants.

Key Questions and Reflections

This study raises several important questions that are not fully addressed. The interaction between the dual-core spacing and the coating composition is not investigated, despite being a critical factor in determining the final microstructure and properties of the surfacing layer. Additionally, the study does not report on the deposition rate, dilution rate, or residual stress state of the dual-coated electrode surfacing, which are important for evaluating coating quality and durability.

The study also does not compare the dual-coated electrode performance with that of conventional single-core electrodes under identical conditions, making it difficult to quantify the performance advantage. A systematic comparison would provide valuable guidance for process selection in industrial applications.

Furthermore, the study does not address the cost-effectiveness of the dual-coated electrode approach. The dual-core design requires more complex manufacturing, which may increase the electrode cost. The economic benefit of improved welding stability and deposition quality must be weighed against the increased electrode cost.

Study Insights and Conclusions

This paper provides valuable insight into the welding stability characteristics of dual-coated surfacing electrodes, establishing that the dual-core spacing of 1.0 mm, coating weight factor of 45%-56%, welding current of 180-200 A, and electrode-to-workpiece distance of 7 mm produce optimal welding stability and surfacing layer hardness exceeding 6200 HV. The dual-core design offers improved arc stability and deposition uniformity compared to conventional single-core electrodes, but requires precise control of electrode manufacturing parameters and welding process parameters. For engineers in the steel pipe and pipeline industries, this study provides actionable guidance on the use of dual-coated surfacing electrodes for wear protection of critical components. The findings underscore that the dual-coated electrode approach is a promising technology for achieving high-hardness, wear-resistant surfacing layers with consistent quality, provided that the critical process parameters are carefully controlled.